The invention relates to the braking of vehicles, particularly two-wheeled vehicles, by immobilization or retarding action on a moving element such as a wheel, a disc, or a brake drum.
Considering, e.g., the case of a bicycle or motorcycle, known braking devices include control levers mounted on the handlebars and intended to control the action of a plurality of brake pads by means of cables or rods. In general, one brake pad is provided on each side of a wheel, each pair of pads being held by a support furnished with means for pressing the pads against the wheel in order to retard or stop rotation of the wheel.
When the control levers are actuated they cause displacement of the pads toward the rotating moving element(s), until the element(s) are more or less vigorously engaged based on the force applied with the control levers. In this way the pads are brought into and out of contact with the moving element(s); i.e., the initial braking engagement is an all-or-nothing action.
The braking force is adjusted by applying greater or lesser compression force to the control levers; this results in a greater or lesser compression force on the moving element(s).
The force exerted on the rotating moving elements(s), such as a wheel or wheels, for example, is represented more or less directly by a force on the rolling surface of the wheel(s).
While the kinematics and control means remain constant for a given machine, the same is not true of the rolling surface, which virtually always shows constant variation. A blacktop surface has spots of gravel on it, a dry surface has some puddles of water, smooth grass suddenly gives way to mud, etc.
Accordingly, an actuating action on the braking system which may be correct at a given instant may be dangerous at the next instant, and in practice it may not be possible to continuously adjust the force on the control levers by observing the ground. Moreover, conditions which apply to the front wheel may not be applicable to the rear wheel.
Consequently, particularly with regard to the control of braking of the front wheel, not only is there a danger of skidding and loss of control, but the rider may actually be spilled, e.g., by being swung over the handlebars. This is particularly dangerous in the case of a motorcycle or all-terrain vehicle (ATV).
To remedy the problem of locking of the wheels in the case of automobiles there is a known braking system referred to commercially as "ABS", in which sensors employed on the customary automotive brake discs transmit certain information to an electronic circuit whereby the brake pads are retracted from the brake disc before the wheel locks, and then are reapplied into contact with the disc; and this alternating action is continued.
The cycle of exertion of pressure on the brake pads to engage the disc, followed by release of such pressure, is very rapid, enabled by the electronic assistance system. It is much more rapid than if the operator attempted to control the braking himself by applying and then releasing the brake pedal a plurality of times in succession, which technique is sometimes referred to in practice as "pumping the brakes".
The ABS braking system thus enables one to avoid locking of the wheels of the vehicle and to achieve particularly effective and rapid braking over a shorter distance.
However, the ABS braking system is not adaptable to every case, particularly for two-wheeled vehicles in which light weight and low cost are objectives.
Means of improving braking of two-wheeled vehicles based on the idea of pumping the brakes have already been considered.
French Patent No. 2,591,976 provides for complete release of the brake pads with complete suppression of contact between the pad the wheel. This has the serious drawback that the cyclist unconsciously compensates for the total loss of braking by keeping the control lever under compression, thereby rendering the system ineffective, because once an adjustment is made to the gap between the brake pad and the wheel the device returns to the initial braking position, such that the special device only serves at best to retard the locking of the wheel and not to prevent it.
U.S. Pat. No. 4,055,235 is also known, which describes a device intended to increase the braking force.